The present embodiments relate to contrast agent enhanced medical diagnostic ultrasound imaging. In particular, contrast agent imaging adapts over time.
Contrast-agent enhanced ultrasound (CEUS) is a common technique for visualization, diagnosis, and analysis of a variety of organs and pathologies. Contrast agents typically are gas-filled microbubble solutions, which are administered intravenously to a subject. As the contrast agents circulate throughout the subject's vascular system, the microbubbles serve as detectable acoustic reflectors. There are specific ultrasound pulse sequence combinations or types of scans that enhance microbubble detection. As the agents reach tissue, the agents perfuse into the tissue. The tissue is perfused at a rate or in a quantity of agent based, at least in part, on the health of the tissue. Unhealthy tissue (e.g., a tumor or other lesion) may uptake contrast agent to a different extent or rate than surrounding healthy tissues. A region of more substantial uptake may visually appear as a bright (hyper echoic) region compared to the surroundings.
Physiologic and pathologic conditions may be associated with specific contrast agent enhancement patterns. For example, a malignant lesion within the liver may enhance quickly (e.g., uptake at a greater rate or to a greater extent than surrounding tissue), but then “wash out” more quickly. In addition, certain patterns, such as outer to inner enhancement of a lesion or spokewheel like enhancement pattern, are associated with specific diagnoses.
For most contrast agents, the microbubbles disappear from circulation within a short period of time, typically less than 15 minutes. Ultrasound pulses utilized to interrogate the microbubbles may result in bubble destruction. In general, more intense ultrasound waves destroy more microbubbles. As the gas-filled microbubbles circulate through the lungs, their contents are released into the atmosphere, destroying the microbubbles. Microbubbles are also destroyed due to various forces experienced while traveling throughout the vascular system.
Because some enhancement patterns for diagnosis require several minutes to evolve, it is important that a sufficient quantity of microbubbles remain in circulation throughout the time course of a particular pattern. However, in order to observe the pattern, the tissue is monitored with ultrasound scanning fairly continuously. Thus, there is a tradeoff between the observation of microbubbles and their destruction during the observation process. The user may minimize microbubble destruction by maintaining a low mechanical index (MI) of the ultrasound beam, limiting the number of beams utilized to generate a given frame, and minimizing the duration of active imaging.